Rational Aspects of Split Treatment Lime Softening

Split treatment in lime-soda ash water softening is an old and well known process. However, it has been erroneously considered an outdated process since the development of recarbonation equipment. The advantages of split treatment in reduced operating costs and reduced first costs are significant. Split treatment should be considered whenever partial magnesium removal is required to achieve water quality objectives. The concepts concerning split treatment presented in this paper include: A simple rational method of calculating the percentage of flow that should by-pass the first stage, the method of calculating the chemical dosages based on the full plant flow, and the method of calculating the excess lime concentration that results in the first stage from the by-passed flow. Application of these concepts should encourage better design and operation of split treatment plants.